Oxygen-rich hierarchically porous carbons are prepared by employing one-step KOH activation of pitch based oxidized spheres (POS) as carbon precursors. The activation temperatures not only allow directed tailoring the porosity of carbon but also guarantee the preservation of moderate oxygen functional groups from POS, which are beneficial for efficiently integrating the electrical double layer capacitance and pseudocapacitance in one electrode. The as-prepared pitch-based activated carbons (PAC) possesses a high specific surface area of 2245 m(2) g(-1) with well-developed micropores, appropriate meso-macropores, and rich oxygen doping of 15.9 at%. Benefiting from the synergistic effect of hierarchical porosity and pseudocapacitive oxygen groups, PAC exhibit high specific capacitance of 427F g(-1) and 302F g(-1) at 0.5 A g(-1) and 50 A g(-1), respectively, as well as excellent capacitance retention of 71% in a three-electrode system with 6 M KOH electrolyte. Moreover, the as-assembled symmetrical supercapacitor displays a high energy of 5.79 Wh kg(-1) at a power density of 9918 W kg(-1) with excellent cycling stability with capacitance retention of 95% at 5 A g(-1) after 10,000 cycles, which is higher than that of commercial Kuraray YP-50F. This finding demonstrates that one-step KOH activation coupled with oxygen-rich pitch may act as an optimal component to finely tailor the porosity and oxygen doping on activated carbons for energy storage applications. (C) 2019 Elsevier Inc. All rights reserved.